Square and rectangular ducting are widely used in HVAC systems. Such ducting can be located in a floor or ceiling, for example, between floor or ceiling joists, whereas ducting of other cross-sectional shapes, such as round, may not fit in such locations and still be sufficiently large enough in size to handle the HVAC load required.
Referring to FIGS. 1-3, it is known to manufacture square and rectangular ducting structures such as structure 20, by bending a sheet of thin-gauge material to form the corners and the four walls of a length of ducting 22 and then join the duct together along one corner 24 to form an integral structure. This corner joint may take various forms, such as by overlapping portions of the ducting and then screwing the overlapped portions together, or by utilizing an “S” shaped flange 26 or other shaped member to join the ducting along corner 24. Typically, lengths of square and rectangular ducting produced in this manner are relatively limited in length due to the size of the brake press or other machinery used to form the corners of the ducting and also limited by the length of the sheet metal stock available, typically about four feet in length.
Because square and rectangular cross-section HVAC ducting is typically of relatively short lengths, it is necessary to connect ducting sections end-to-end to achieve a desired overall length. In this regard, as shown most clearly in FIGS. 1 and 2, a face flange structure 28 is integrally formed at the ends of each wall of the duct 22. The face flange structure typically has a mating or face section 30 extending perpendicularly to the corresponding wall of duct 22 and a reinforcement hem structure 32 extending transversely from the distal edge flange face 30. The hem structure 32 may be folded over on itself to form a double thick section for additional strength. In FIG. 1, the hem structure 32 is folded inwardly on itself whereas in FIG. 2, the hem section is folded outwardly on itself.
As will be appreciated by the foregoing construction, it is not possible to extend the face flange structures 28 to occupy the entire corner at the juncture between two adjacent panels of the ducting structure 20. Such open corners are “filled in” by an angle bracket 34 that typically nests with the adjacent portions of the face flange structures 28. FIG. 1 shows the angle brackets 34 prior to installation, whereas FIG. 2 illustrates the angle brackets in installed positions. The angle brackets include corner apertures 35 for receiving a hardware fastener 36 therethrough. The hardware fastener may be in the form of a threaded screw 36 that mates with a nut 38. In this manner, the face flange structures 28 are connected together in face-to-face relationship at the corners of the ducting structure 20.
A flat or other shaped gasket 40 may be interposed between adjacent flange faces 30 in an effort to provide an airtight seal therebetween. A sufficient seal usually is not achieved through the use of only the angle brackets 34. As such, typically, formed clips 41 are also used to also retain the adjacent face flange structures 28 together in an engaged face-to-face relationship. As shown in FIG. 2, the clips 40 are shaped and sized to wrap around the reinforcement hem structures 32 of the face flange structures 28.
Referring to FIG. 3, typically reinforcing members are needed to increase the structural integrity of ducting sections 20 and to prevent the ducting sections from unduly vibrating. FIG. 3 illustrates such reinforcing members in the form of “Z” brackets 39 that extend transversely across duct 22, with one of the flange sections of the brackets attached to the duct by hardware members, welding or otherwise.
Referring to FIG. 4, duct sections 20a and 20b can be interconnected by various slip joint-type connectors. One such connector is shown in FIG. 5 which is a partial cross-section of FIG. 4. In FIG. 5, the connector 42 is generally formed in a “C” shape. The adjacent ends of the duct sections 20a and 20b are turned over on itself to form lip sections 43 to engage with the connector 42. As can be appreciated, a fair amount of effort is required to install the connector 42 in the field since the connector must be slipped over the lips 43. Moreover, corner pieces 44 are required at the corner of the duct sections since the connectors 42 cannot fully close off the corners of the adjacent duct sections, rather connectors 42 stop about a couple of inches short of the corners of the duct sections.
A further slip joint-type connector 45 is shown in FIG. 6, which figure is a cross-sectional view similar to FIG. 5. Connector 45 is generally S-shaped and requires that the adjacent ends of the duct sections 20a′ and 20b′ overlap somewhat. As in connector 42, the S-shape connector 45 is formed in straight lengths and positioned along each side of the ducting. As will be appreciated, this type of connection also does not close off the corners of the duct section 20a′ and 20b′. As such, separate corner pieces corresponding to corner pieces 44 are required to be used in connection with connector 45.
A further slip type connector 46 is shown in FIG. 7. Connector 46 is of a generally S-type connector similar to connector 45, but with a transverse section 47 which is said to increase the stiffness of the connector. The transverse section is formed by bending the connector material over on itself. As in connector 45, the connector 46 can only be used within about two inches of the corner of the duct. As such, separate corner pieces, not shown, are also required with connector 46. Also as with connector 45, installing the connector 46 in the field is not always easy since the connector must engage overlapping sections of the duct and then a fastener must be extended through the overlapped sections of the duct as well as through the connector 46 itself. This requires screws or other hardware members passing through at least five layers of material.
It can be appreciated that the prior art ducting structure shown in FIGS. 1-7 is time consuming and expensive not only to fabricate, but also to assemble and install in the field. The present invention is directed to more economical and faster methods for manufacturing, assembling and installing HVAC ducting of a rectangular or square cross-section.
It is also known to form relatively small size square and rectangular ducts from steel galvanized spiral round ducting or aluminum flexible round ducting. Such ducting is typically in the size of 3-inch×10-inch or 4-inch×12-inch, used primarily for concrete encased toilet and kitchen exhaust ducting. Such ducting is first formed in round cross-section and then stretched to a rectangular shape using sharp, square corner dies having a corner radius of ⅛ inch or less. Such dies perform adequately for relatively small sized ducting where the material is able to flow around the sharp corners of the die. A significant friction resistance occurs between the die corners and the ducting material, but in the relatively small sizes, having from 3 inches to 4 inches along a minor side of ducting, such friction force is typically not so excessive that the ducting material tends to adhere or stick to the corner of the die or the material tends to split at the corner due to the high friction-caused tension existing between the die corner and the ducting material. However, for larger size ducting, for example, having a minor width of 6 inches or more, the friction between the sharp corner of the die and the ducting material becomes excessive, causing the ducting material to seek to “adhere” to the die corner, which can cause the material to excessively stretch and thereby split or otherwise fail during the attempt to reconfigure the round cross-section into a rectilinear cross-section. Also, the large friction load on the die often causes the die to twist or otherwise deform due to the ducting material “catching” on the corners of the die.